1. Field of the Invention
The present invention relates generally to a process for casting a cylindrical product and, more particularly, to such a casting process which, when implemented, provides a cylindrical product having a wear-resistant outer surface at its radial extremities.
2. Description of the Prior Art
National transportation objectives include the conservation of fuel by increasing the efficiency of automobiles and reducing toxic airborne automobile emissions. Suggested ways to improve internal combustion engine efficiency are to downsize the overall weight of automobiles and to reduce the mass of rotating engine parts such as camshafts to minimize the energy that is expended to overcome friction and rotational inertia.
Presently, most camshafts are made of iron or steel by forging or casting, using conventional forging or casting techniques. As is well known in the art, iron or steel camshafts perform the job of opening and closing valves through millions of cycles and rarely require replacement. Thus, reliability, maintenance and the general performance of conventional automobile camshafts are not concerns. However, it is well recognized that iron or steel camshafts greatly increase overall engine weight.
In order to downsize the overall weight of automobiles and reduce the mass of various rotating engine parts, lighter-weight camshafts have been proposed. One proposal utilizes powder metallurgy (PM) cams and a tubular steel shaft. The shaft is inserted through holes in the cams. After positioning the cams for proper alignment, a mandrel is passed through the shaft and expanded to press fit and lock the cams to the shaft. Afterward, the mandrel is relaxed and removed. Other conventional materials have been suggested for use in the manufacture of automobile camshafts to reduce their weight. For example, the use of magnesium and aluminum have been proposed. However, while economically feasible on a first-cost basis, neither of these materials possess, in their pure form, the inherent strength, durability and wear resistance required for sustained performance and are not acceptable without some form of alteration.
With the knowledge of the inherent weakness of pure aluminum in mind, lighter weight automobile camshafts have been made utilizing aluminum that contains added strengtheners such as particles and fibers. Unfortunately, these aluminum additions to increase wear resistance utilizing presently known addition processes have not been successful. Neither have efforts to increase the wear resistance of aluminum via surface treatment techniques been successful due to the costs associated with implementing these techniques.
As can been seen from the foregoing, efforts to reduce the weight of automobile engine parts such as camshafts utilizing light weight metals like pure magnesium and aluminum to increase the efficiency of automobile engines have met with little success. Consequently, there is a need for an improved process for manufacturing automobile camshafts which may be implemented using light weight metals such as magnesium and aluminum to reduce camshaft weight. This improved process must be capable of imparting to the camshaft the strength, durability and wear resistance qualities necessary to allow an aluminum or magnesium camshaft to sustain the millions of operating cycles seen in conventional automobile engines without failure.